So, with the advent of weather on my friend's SMP server, two structures have already been burned to the ground by lightning strikes. Miraculously, the current tallest flammable structure on the server is unharmed. The observation deck of my lighthouse is made of red wool (I've converted the white wool base to iron). I've also made sure to put a firebreak (triple row of glass floor) between the wooden access-way and the wooden stairs inside the structure, so while a lightning strike wouldn't be completely disastrous, the top section is the most time consuming to build. So, for some reason, I got the idea that lightning only strikes vertically, which led me to build a glass shield at the ceiling of the map, in the shape of the widest parts of the lighthouse.

You can see the shield towards the top of the image. It's placed directly above the structure, and provided lightning only travels vertically downward, protects the entire structure.

4 Answers
4

The thunderbolts do strike diagonally, but most of the time it strikes like the picture below.

There are also times when it will strike diagonally.

I recommend that you extend the glass shield to about 10x10 so that the lightning will not hit it at all (lightning should not be struck at an angle of more that 45 degrees)

Also, wooden stairs do not burn.

EDIT:

I tried manipulating the lightning again. I used zombe's modpack to manipulate the lightning by using the weather control (turned on thunderstorm with mayhem modifier which increases the frequency of lightning). However if you use single player command's "weather lightning" command
, it will go through anything.

So I decided to do an actual test with wood and a glass canopy.

Then I turned on lightning with mayhem modifier. It didn't strike through the canopy.

As you can see it DID NOT pass through. In the end, my wood was in PERFECT condition. none of it was burned.

@bckbck Can you give me a hard value for the maximum strike angle?
–
GnomeSliceMay 1 '11 at 18:57

@gnomeslice i'll try to dig thru the source code and see what i can find.
–
user8949May 2 '11 at 0:31

@bckbck I'm going to award you the bounty in good faith that you'll deliver on the angles.
–
GnomeSliceMay 2 '11 at 3:27

2

@gnomeslice im still digging through the code. no hard evidence of the angles so far, otherwise i'll use a protractor (i measured, it is 25º). also currently i have my exams till the end of next week, so it may be delayed
–
user8949May 4 '11 at 12:34

4

What I'm still not sold on though, is whether or not this angled lightning is just DRAWN this way, or if it actually acts as though it were striking on an angle.
–
GnomeSliceAug 7 '11 at 16:11

This post seems to indicate that it does - linked is a YouTube video where you can see the lightning hitting the ground underneath trees.

Your building could possibly get hit, you may want to build some more protection..

EDIT 2:

Unfortunately, all the testing I did below was in vain - the mod I was using to induce the lightning seems to be causing it to pass through everything up to its target. Till I find proof that vanilla Minecraft lightning does this, I'm revoking the below answer :(

Thanks bckbck for spotting this

EDIT:

I've gone back and done some testing to see if lightning can hit stuff that is protected by shields at varying heights.

My precious wood pile ready to be sacrificed:

I built a shield (10x10), made of sandstone at level 50, and forced lightning to hit.

I found that the lightning would either go round the shield, or strangely, THROUGH it!

After repeated tests, it became obvious that my pitiful shield wasn't enough, the wood kept burning up - so I built another one at 100 blocks high, again 10x10 in size.

Even with this shield, the wood was still getting set on fire, so I expanded the shield on layer 100 to 25x25.

Again I found that the lightning would strike through the shield, so with a final attempt to make my poor wood pile safe, I put a layer of cobblestone on top:

No luck..

My conclusion is that it doesn't matter if lightning strikes on an angle, since it looks like lightning will strike through the shield anyway.

Also, it looks like the visuals are on an angle and the lightning is cast straight downwards ... if you read the post later someone points out that the lightning did not strike under the tree at all.
–
Sadly NotApr 27 '11 at 18:23

It looks like, or is rendered to strike on an angle, but actually it only happens at the vertically highest (up to 127) solid block at its horizontal location. In other words, the lightning travels vertically downward through non-solid transparent blocks with a few exceptions you won't care. This is a theory from code reading, and it seems bckbck has verified this.